Selective reduction type high temperature superconductor and methods of making the same

ABSTRACT

Proposed are a selective reduction type high temperature superconductor and methods of making the same, the superconductor having a pair of charge supply layers each formed of a Cu1-xMx surface ( 1, 1 ), a first superconducting layer formed of a 5-coordination CuO2 surface ( 2 ) and a second superconducting layer formed of a 4-coordination CuO2 surface ( 3 ). Reducing M ions (e.g., Tl ions) in the charge supply layers by heat treatment in a reducing atmosphere enables the 5-coordination CuO2 surface ( 2 ) as the first superconducting layer to be over-doped and the 4-coordination CuO2 surface ( 3 ) as the second superconducting layer to be optimum-doped. According to the present invention, a high temperature superconductor is provided that with its critical temperature held high has a reduced superconducting anisotropy γ, and provides a high critical current density Jc and a high c irreversibility field Hirr.

TECHNICAL FIELD

This invention relates to a selective reduction type, high temperaturesuperconductor, which is a copper (Cu) oxide, high temperaturesuperconductor that permits doping with positive holes by selectivelyreducing constituent elements (atoms). This superconductor can be usedin large scale superconducting power transmission, superconducting powerstorage or reserve, superconducting electronics such as a highperformance Josephson device, a high frequency device or the like. Theinvention also relates to methods of making such a superconductor.

BACKGROUND ART

Conventional Cu-oxide family, high temperature superconductors have beenprepared doping with positive holes, by oxidation, to raise the contentsof the superconducting carriers. Such a high temperature superconductor,however, may cause the carriers to reduce in concentration due todiffusion or bleeding of oxygen atoms by increased temperature. Thisleads to a depletion in superconductivity of the superconductor.

Also, doping with positive holes to obtain a higher carrierconcentration has been thought to require a higher oxygen partialpressure, and it has so far been unattainable to prepare asuperconductor of the type described by doping with positive holes toraise the carrier concentration in a reduction process conditioned underlow partial pressure or vacuum. Since it has been found impossible toincrease the concentration of positive holes by reduction, i.e., bylowering the oxygen partial pressure, the conventional high temperaturesuperconductors have the problem that they have a limited carrierconcentration and are thus low and unsatisfactory in theirsuperconducting properties that include the critical temperature Tc,critical current density Jc, irreversible magnetic filed Hirr. It hastherefore been sought to, solve the problem of bringing into realizationa high temperature superconductor of a reduced oxygen concentration.

With these problems taken into account, it is accordingly a first objectof the present invention to provide a selective reduction type, hightemperature superconductor that permits doping with positive holes byselectively reducing constituent elements (atoms).

Another object of the present invention is to provide a method of makinga selective reduction type, high temperature superconductor.

DISCLOSURE OF THE INVENTION

In order to achieve the first object mentioned above, there is providedin accordance with the present invention, a selective reduction, hightemperature superconductor, wherein it has a portion of its constituentelements selectively reduced whereby it has a superconducting layerthereof doped with positive holes.

The present invention also provides a selective reduction type, hightemperature superconductor that has a portion of its constituentelements selectively reduced whereby there are formed in superconductinglayers a first and a second region doped overly and doped optimally withsuperconducting carriers, respectively.

The present invention further provides a selective reduction type, hightemperature superconductor that has a portion of its constituentelements selectively reduced whereby the superconductor as a whole has asuperconducting carrier concentration such that it is held doped overlyor doped optimally with superconducting carriers.

The present invention also provides a selective reduction type, hightemperature superconductor that has on each of an upper and a lowersurface of a unit lattice thereof a charge supply layer having each of aportion of Cu atoms substituted with a selectively reducible atom.

The present invention also provides a selective reduction type, hightemperature superconductor in which the said superconducting layers havean upper and a lower surface constituted by a CuO₂ layer of5-coordination and a layer other than the upper and lower constituted bya CuO₂ layer of 4-coordination, the said CuO₂ layer of 5-coordinationand 4-coordination having been over- and optimum-doped, respectively, byselective reduction.

Further, the present invention provides a selective reduction type, hightemperature superconductor having a selectively over-doped and/or aselectively optimum-doped construction.

The present invention further provides a selective reduction type, hightemperature superconductor, characterized in that it is made of a (Cu,M) group, high temperature superconducting material, which can bedescribed by composition formula:

Cu_(1−x)M_(x)(Ba_(1−y),Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w)

where M represents ions of one or more polyvalent metallic elementsselected from the class which consists of Tl, Bi, Pb, In, Ga, Sn, Ti, V,Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, W, Re and Os; L represents one or moreelements selected from the class which consists of Mg and alkalinemetallic elements; 0≦x≦1.0; 0≦y≦1; 0≦z≦1; 0≦w≦4; and 1≦n≦16.

The present invention also provides selective reduction type, hightemperature superconductor, characterized in that it is made of a (Cu,Tl) group, high temperature superconducting material that can bedescribed by composition formula:

Cu_(1−x)Tl_(x)(Ba_(1−y)Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w)

where L represents one or more elements selected from the class whichconsists of Mg and alkaline metallic elements; 0≦x≦1.0; 0≦y≦1; 0≦z≦1;0≦w≦4; and 1≦n≦16.

The present invention also provides a selective reduction type, hightemperature superconductor, characterized in that it is made of a (Cu,Tl) group, high temperature superconducting material that can bedescribed by composition formula:

Cu_(1−x)Tl_(x)(Ba_(1−y)Sr_(y))₂(Ca_(1−z)L_(z))₂Cu₃O_(10−w)

where L represents one or more elements selected from the class whichconsists of Mg and alkaline metallic elements; 0≦x≦1.0; 0≦y≦1; 0≦z≦1;and 0≦w≦4.

The present invention also provides a selective reduction type, hightemperature superconductor, characterized in that it is made of a hightemperature superconducting material that can be described bycomposition formula:

Cu_(1−x)Tl_(x)(Ba_(1−y)Sr_(y))₂(Ca_(1−z)L_(z))₃Cu₄O_(12−w)

where L represents one or more elements selected from the class whichconsists of Mg and alkaline metallic elements; 0≦x≦1.0; 0≦y≦1; 0≦z≦1;and 0≦w≦4.

The present invention further provides a selective reduction type, hightemperature superconductor, characterized in that selective over- oroptimum-doping is effected by decrease in the valence number of ions ofa constituent element by decrease in the oxygen concentration, that isby selective reduction, or by varying (increasing or decreasing) oxygenconcentration.

The present invention also provides a selective reduction type, hightemperature superconductor, characterized in that it is a selectivelyover-doped type or a selectively optimum-doped type, high temperaturesuperconductor in which n is any one of 3, 4, 5, 6 and 7.

The present invention further provides a selective reduction type, hightemperature superconductor having a construction that the reduction ofselectively reducible ions causes the ions in the charge supply layersto receive electrons in their outer shell orbits, thereby providingholes in the CuO₂ layer of 5-coordination of a said superconductinglayer.

The present invention further provides a selective reduction type, hightemperature superconductor having a construction that it has asuperconducting anisotropy of not greater than 10 and a coherencedistance of not less than 3 angstroms.

The present invention further provides a selective reduction type, hightemperature superconductor having a construction that said selectivereduction transforms its natural superconducting wave function that isof a d-wave high in spatial anisotropy to a wave function of a (d+is)wave that has also a property of an s-wave lacking of spatialanisotropy.

A selective reduction type, high temperature superconductor soconstructed as mentioned above according to the present invention can beprepared in a reducing atmosphere or can in use have its oxygen contentdecreased, yet still maintain a high critical temperature Tc, whileproviding a reduced aniso-superconductivity γ, a high critical currentdensity Jc and a high critical magnetic field Hirr.

Stated otherwise, a selective reduction type, high temperaturesuperconductor according to the present invention is provided with acrystalline and an electronic structure that permits achieving improvedJc and Hirr while maintaining Tc high. Moreover, provided with asuperconducting wave function of a (d+is) wave, it is low insuperconducting anisotropy. With these advantages, it can be used as ahigh performance, high temperature superconductor in a variety ofindustrial sub-fields concerned.

In order to achieve the second object mentioned above, the presentinvention provides a method of making a selective reduction type, hightemperature superconductor, which comprises the steps of: preparing ahigh temperature superconductor, and heat-treating the prepared hightemperature superconductor in a reducing atmosphere.

The present invention also provides a method of making a selectivereduction type, high temperature superconductor, comprising the stepsof: using an amorphous film as a precursor of high temperaturesuperconductor; causing the amorphous film to grow epitaxially byamorphous phase epitaxy; and heat-treating in a low oxygen, reducingatmosphere the amorphous film that has grown epitaxially.

The present invention further provides a method of making a selectivereduction type, high temperature superconductor, comprising the stepsof: causing added constituent elements to develop their self-assembling(or self-forming) effect; and causing the high temperaturesuperconductor to grow epitaxially by the self-assembling effect.

A method of making a selective reduction type, high temperaturesuperconductor of the present invention as mentioned above is applicableto making a (Cu, M) group, selective reduction type, high temperaturesuperconductor expressed by composition formula:

Cu_(1−x)M_(x)(Ba_(1−y),Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w)

where M represents ions of one or more polyvalent metallic elementsselected from the class which consists of Tl, Bi, Pb, In, Ga, Sn, Ti, V,Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, W, Re and Os; L represents one or moreelements selected from the class which consists of Mg and alkalinemetallic elements; 0≦x≦1.0; 0≦y≦1; 0≦z≦1; 0≦w≦4; and 1≦n≦16.

A method of making a selective reduction type, high temperaturesuperconductor of the present invention as mentioned above is alsoapplicable to making a (Cu, Tl) group, selective reduction type, hightemperature superconductor expressed by composition formula:

Cu_(1−x)Tl_(x)(Ba_(1−y)Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w)

where L represents one or more elements selected from the class whichconsists of Mg and alkaline metallic elements; 0≦x≦1.0; 0≦y≦1; 0≦z≦1;0≦w≦4; and 1≦n≦16.

A method of making a selective reduction type, high temperaturesuperconductor of the present invention as mentioned above is alsoapplicable to making a (Cu, Tl) group, selective reduction type, hightemperature superconductor expressed by composition formula:

Cu_(1−x)Tl_(x)(Ba_(1−y)Sr_(y))₂(Ca_(1−z)L_(z))₂Cu₃O_(10−w)

where L represents one or more elements selected from the class whichconsists of Mg and alkaline metallic elements; 0≦x≦1.0; 0≦y≦1; 0≦z≦1;and 0≦w≦4.

A method of making a selective reduction type, high temperaturesuperconductor of the present invention as mentioned above is alsoapplicable to making a selective reduction type, high temperaturesuperconductor expressed by composition formula:

Cu_(1−x)Tl_(x)(Ba_(1−y)Sr_(y))₂(Ca_(1−z)L_(z))₃Cu₄O_(12−w)

where L represents one or more elements selected from the class whichconsists of Mg and alkaline metallic elements; 0≦x≦1.0; 0≦y≦1; 0≦z≦1;and 0≦w≦4.

A method of making a selective reduction type, high temperaturesuperconductor of the present invention so constructed as mentionedabove permits manufacturing a positive hole dopable or doped selectivereduction type, high temperature superconductor.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will better be understood from the followingdetailed description and the drawings attached hereto showing certainillustrative forms of embodiment of the present invention. In thisconnection, it should be noted that the embodiments illustrated in theaccompanying drawings hereof are intended in no way to limit the presentinvention but to facilitate an explanation and understanding thereof.

In the drawings:

FIG. 1 is a diagram showing modeled crystalline structures of aselective reduction type, high temperature superconductor according tothe present invention in which A and B show unit lattices with n=1 andn=2, respectively;

FIG. 2 is a diagram showing modeled crystalline structures of aselective reduction type, high temperature superconductor according tothe present invention in which A, B and C show unit lattices with n=3,n=4 and n=5, respectively;

FIG. 3 is a diagram showing the temperature dependency of the electricalresistivity according to a first form of embodiment of the presentinvention annealed at various temperatures in a nitrogen atmosphere;

FIG. 4 is a diagram showing thermo-analysis data according to the firstform of embodiment of the invention;

FIG. 5 is a diagram showing change of the hole concentration withtemperature according to the first form of embodiment of the inventionannealed in nitrogen atmosphere;

FIG. 6 is a diagram showing relationships between Tc, normal conductionelectrical resistivity, carrier concentration, weight's rate of changeof, and annealing temperature for, specimens according to the first formof the invention annealed in nitrogen atmosphere;

FIG. 7 is a diagram showing an electronic state according to the firstform of embodiment of the invention that is high in oxygenconcentration;

FIG. 8 is a diagram showing an electronic state according to the firstform of embodiment of the invention that is low in oxygen concentration;and

FIG. 9 is a diagram showing an X-ray diffraction analysis patternaccording to a second form of embodiment of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention for a selective reduction type, hightemperature superconductor and a method of its making will be describedin detail with respect to suitable forms of embodiment thereofillustrated in FIGS. 1 to 9.

While the conventional methods for increasing the carrier concentrationin a high temperature superconductor rely either on oxidation by heattreatment in high pressure oxygen or on substitution to form elements ofvarying valence numbers, a selective reduction type, high temperaturesuperconductor according to the present invention is characterized inthat it has an increased concentration of positive holes achieved byreduction, namely by lowering the oxygen concentration, which permitsenhancing its Tc (critical temperature), Jc (critical current density)and Hirr (critical magnetic field) to a considerable extent.

A Cu-oxide super conductor of the present invention:

Cu_(1−x)M_(x)(Ba_(1−y),Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w)

includes charge supply layers formed by Cu_(1−x)M_(x) plane that make upthe upper and lower surfaces of a unit lattice, and superconductinglayers that make up the other layers (other than the upper and lower) ofthe unit lattice, namely those formed by CuO₂ planes of a pyramidal CuO₅cluster, i.e., CuO₂ planes of 5 coordination number and those formed byCuO₂ planes of a planar CuO₄ cluster, i.e., CuO₂ planes of 4coordination number, these different superconducting layers being laidalternately one on another.

FIGS. 1 and 2 illustrate modeled crystal structures of selectivereduction type, high temperature superconductors of the presentinvention. These modeled crystal structures are illustrated for aCuBaCa_(n−1)O_(2n+4−w) where 1≦n≦16 and 0≦w≦4, in particular withrespect to examples thereof in which n is an integer from 1 to 5.

FIG. 1A is for a unit lattice where n is 1, and FIG. 1B is for a unitlattice where n is 2. In FIG. 2, A, B and C are for unit lattices wheren is 3, 4 and 5, respectively.

Referring to FIG. 2A, a selective reduction type, high temperaturesuperconductor of the present invention comprises a pair ofCu_(1−x)M_(x) planes 1, 1 that constitute its charge supply layers, aCuO₂ plane 2 of 5 coordination number that constitutes a superconductinglayer and a CuO₂ plane 3 of 4 coordination number that constitutes asuperconducting layer.

According to a selective reduction method of the present invention, asuperconducting layer is formed as a CuO₂ plane 2 of coordination number5 in which the density of positive holes is such that it is eitheroverly (excessively) or optimally doped with them, or nearly so doped,and is formed as a CuO₂ plane 3 of coordination number 4 in which thedensity of positive holes is such that it is optimally or nearlyoptimally doped with them. To wit, the method permits forming anexcessively or optimally doped CuO₂ plane and an optimally doped CuO₂plane selectively and separately.

A selective reduction method of the present invention is a methodwhereby polyvalent, reducible ions (e.g., Tl ion) substituted for aportion of Cu ions in the charge supply layers of a high temperaturesuperconductor are reduced (their ionic valence is reduced) bydecreasing the oxygen content in the high temperature superconductor(e.g., by heat treatment in a reducing atmosphere). It is by thisreduction of reducible substituted ions that the electronic and bandstructures of a Cu-oxide high temperature superconductor vary and amechanism is revealed that permits doping with positive holes. It shouldalso be noted at this point that term “selective reduction type hightemperature superconductor” as used herein, of the present invention isintended to refer to a high temperature superconductor that comprises apair of charge supply layers constituted by an upper and a lower surfaceof a unit superconductor lattice having each of a portion of Cu atoms Ithese surfaces substituted with polyvalent, reducible ions and havingthese substitutional ions exclusively and selectively reduced, and asuperconducting layer as a layer other than those upper and lowersurfaces.

FIG. 7 is a diagram that shows an electronic state of the CuO₂ plane 2of an afore-mentioned Cu-oxide, high temperature superconductor in caseits oxygen content is high, and FIG. 8 is a diagram that shows anelectronic state of the CuO₂ plane 2 of an afore-mentioned Cu-oxide,high temperature superconductor in case its oxygen content is decreased.

Referring to FIGS. 7 and 8, if the oxygen content is high it is seenthat Tl ions present in a charge supply layer is in a plus (+) trivalentstate and the Tl6 s level is above the Fermi level. If as a result ofoxygen reduction the oxygen content is lowered, Tl ions take a plusmonovalent state and the Tl6 s level lies below the Fermi level.

As a consequence, electrons are pulled out of the CuO₂ plane ofcoordination number 5 as a superconducting layer and holes are suppliedinto the CuO₂ plane of coordinate number 5, the superconducting layer.In this way, reducing reducible polyvalent ions such as Tl ions bydecreasing the oxygen content, namely supplying positive holes byselective reduction permits increasing the carrier concentration. In thecontext hereof, supplying positive holes by selective reduction isreferred to as selective doping.

Using selective doping enables producing a high performance, hightemperature superconductor. For example, heat-treating in a reducingatmosphere such a high temperature superconductor formed in an overlydoping composition to decrease oxygen by a certain amount decreases thecarrier concentration because of the superconducting layers losingoxygen, but permits the CuO₂ plane 2 of coordination number 5 as onesuperconducting layer to stay in an overly doped state by being injectedwith holes by selective doping.

On the other hand, the 4-coordination CuO₂ plane 3 providing for theother superconducting layer is not doped with holes and therefore has areduced carrier concentration, staying in an optimally doped state.Thus, a makeup is provided in which while the superconducting layers asa whole are overly doped, there also exists an optimally doped CuO₂plane. The method mentioned above is referred to herein as selectiveover-doping method. Likewise, it is also possible to make both the5-coordination and 4-coordination CuO₂ plane superconducting layersdoped optimally as a whole in their carrier concentration. Thisalternative method is referred to herein as selective optimum dopingmethod.

A difference in potential level between more than one types of CuO₂planes and a difference in energy level between the bands which theseCuO₂ planes possess can be used in this manner to permit the over-dopedCuO2 plane and the optimum-doped to coexist in a unit lattice, and thusto have Tc, Jc and Hirr of the superconductor raised considerably.

By the way, Tc varies with respect to the amount of doping,parabolically or along a parabolic curve opening downwards, whereon theoptimum doping is established at the amount of doping at which Tcbecomes maximum. In the case of Cu-oxide high temperaturesuperconductors, this corresponds to the number of holes for one Cu(atom) that is 0.2 to 0.23. Further, over-doping indicates the amount ofdoping that is greater than that for optimum doping. Using the selectiveover-doping method according to the present invention gives rise toover-doping as a whole, but by the presence of an optimum-dopedsuperconducting layer as mentioned above does not lower Tc despiteover-doping.

Thus, in a Cu-oxide, selective reduction type, high temperaturesuperconductor of the present invention, use is made of a change in theelectronic and band structures formed by substitution of polyvalentreducible ions, e.g., Tl ions, for a portion of Cu ions in the chargesupply layers to realize a mechanism that permits selective doping withpositive holes.

This mechanism in a selective reduction type, high temperaturesuperconductor of the present invention despite shortage of oxygen inthe superconducting layers or against the inability to enough supplythem with oxygen in the preparation step of the superconductor causesthe substitute ions to pull electrons out of the superconducting layersand thus to supply them with positive holes. Accordingly, there resultshere no deterioration in properties as does if oxygen comes off, andthen the preparation in an atmosphere of low oxygen partial pressurestill permits yielding a high temperature superconductor of highperformance.

Further, given the superconducting layers formed in an over-doped stateas suitably composed and structured, the use of this mechanism wherebyselective doping by selective reduction permits the 5-coordination CuO₂plane to stay over-doped while rendering the 4-coordination CuO₂ planeoptimum-doped makes it possible to raise Jc while at the same timeholding Tc high. In this case, the superconducting layers may, assuitably composed and structured, be formed also in an optimum-dopedstate.

While both optimum-doping and over-doping are described above as beingcontrollable by decrease in the valence number of Tl ions by reductionin oxygen content, it is, of course, possible to control them byincrease and decrease in oxygen content.

A selective reduction type, high temperature superconductor of thepresent invention as described above can be made first by preparing ahigh temperature superconductor by using high pressure synthesis, hotpressing, spattering, laser ablation or the like irreversible ornon-equilibrium process of manufacture, and then by subjecting it toreduction heat-treatment.

The above-mentioned method of making according to the present inventionis applicable to making selective reduction type, high temperaturesuperconductors as can be described by the composition formula (a)mentioned below. Composition Formula (a):

Cu_(1−x)M_(x)(Ba_(1−y),Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w)

where M represents ions of one or more polyvalent metallic elementsselected from the class which consists of Tl, Bi, Pb, In, Ga, Sn, Ti, V,Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, W, Re and Os; L represents one or moreelements selected from the class which consists of Mg and alkalinemetallic elements; 0≦x≦1.0; 0≦y≦1; 0≦z≦1; 0≦w≦4; and 1≦n≦16.

The above-mentioned method of making according to the present inventionis further applicable to making selective reduction type, hightemperature superconductors as can be described by the compositionformula (b) mentioned below. Composition Formula (b):

Cu_(1−x)Tl_(x)(Ba_(1−y)Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w)

where L represents one or more elements selected from the class whichconsists of Mg and alkaline metallic elements; 0≦x≦1.0; 0≦y≦1; 0≦z≦1;0≦w≦4; and 1≦n≦16.

In order to prepare thin films of a Cu-oxide superconductor:

Cu_(1−x)M_(x)(Ba_(1−y),Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w)

having a layer structure according to the present invention, it isnecessary that charge supply layers and superconducting layers be laidone on another alternately. Also required is that each layer be formedunder accurate control of its composition and crystallinity and be of alarge area.

This in turn requires, in addition to physical control such as fortemperature and pressure, that additional element M exhibit itsauto-forming capacity and that the crystal periodicity and atomicordering in the CuO₂ plane and in the direction perpendicular thereto beenhanced to an ideal level. An improvement in the in-plane ordering bythe epitaxial effect an improvement in the crystallinity in the planeand in the direction perpendicular thereto by the chemicalauto-formation effect of the additional element M result in a largeimprovement in the atomic ordering in the thin film crystal, which inturn contributes to a rise in superconductivity. An example of theadditional element M is the utilization of M=Tl which possesses thestructure stabilizing effect, the reaction accelerating effect, thecharge supply effect and the Tc increasing effect together incombination. This additional element M has been found to exhibit thesame or similar effects in forming high temperature superconductorsother than those mentioned above. The method of making according to thepresent invention is designed to utilize the effects described above.

It should further be noted that a high temperature superconductingmaterial according to the present invention possesses a d-wavesuperconductivity by being a material that is large in Coulomb repulsionand of strong correlativity. As a result, it is considerably large insuperconducting anisotropy in the CuO₂ plane. This anisotropy can bemade smaller by the selective reduction of the present invention. Towit, as shown in FIG. 8, performing the selective reduction bringselectrons in the CuO₂ plane into a [d+is] state where an s-wave propertyis introduced that is characteristic of a superconducting material ofweak correlativity. This leads to realization of a high performancesuperconducting material that is small in anisotropy.

It is thus seen that the method of making according to the presentinvention achieves the preceding effect as well.

Mention is next made of a first, preferred form of embodiment of theinvention represented by an example having a composition:(Cu_(1−x)Tl_(x))Ba₂Ca₂Cu₃O_(y) where 0≦x≦1.0 and 0≦y≦1, and having astructure with a unit lattice illustrated in FIG. 2A. The structure ofspecimen for this first form of embodiment of the invention as indicatedin FIG. 2A is referred to here as Cu-1223.

An explanation is first given in respect of a method of making thisfirst form of embodiment of the invention.

Raw materials to make up a selective reduction type, high temperaturesuperconductor as the first form of embodiment of the invention are:CuO, BaCO₃, CaCo₂, BaO₂ and CaO₂ with an oxidizing agent such as of AgOor CaO₂ and a reducing agent such as of Cu₂O.

First, a precursor of Ba₂Ca₂Cu₂O₇ has CuO and Tl₂O₃ mixed therewith in aproper amount, and a specimen having a composition:(Cu_(1−x)Tl_(x))Ba₂Ca₂Cu₃O_(y)(x=0.5) is prepared by synthesis in acubic angle high pressure generating apparatus under conditions of 85°C., 5 Gpa and 2 hours.

Next, this specimen is annealed in a reducing atmosphere, e.g., ofnitrogen gas, of a temperature range from 400° C. to 700° C., preferablyat 540° C. for a period of 12 hours. This selective reduction treatmentgives rise to a selective reduction type, high temperaturesuperconductor of this form of embodiment of the invention.

What is to be mentioned further is that the above-mentioned method ofmaking according to the present invention is also applicable to makingselective reduction type, high temperature superconductors as can bedescribed by the composition formula (c) mentioned below. CompositionFormula (c):

Cu_(1−x)M_(x)(Ba_(1−y),Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w)

where L represents one or more elements selected from the class whichconsists of Mg and alkaline metallic elements; 0≦x≦1.0; 0≦y≦1; 0≦z≦1;and 0≦w≦4.

An explanation is next given in respect of properties of the first formof embodiment of the invention.

FIG. 3 is a diagram that indicates the temperature dependency of theelectrical resistivity for various temperatures at which annealing iseffected (for specimens) in the first form of embodiment.

As shown in FIG. 3, Tc rises from 97 K to 131 K as the annealingtemperature is raised. The curves' gradient varies somewhat in thevicinity of Tc for the annealing temperatures from 350° C. to 450° C.,apparently due to ununiformity of the specimen. A normal conductionelectrical resistivity rises for the annealing temperature that israised from 200° C. to 400° C., and then falls for the annealingtemperature of 400° C. to 550° C., followed by a rise at the annealingtemperature of 600° C.

FIG. 4 is a diagram showing thermo-analysis data in the first form ofembodiment of the invention. From the results of the thermo-gravimetricanalysis (TG), it is shown that the weight decreases as the annealingtemperature is raised and especially that it falls sharply in thevicinity of 400° C. and in excess of 700° C. From the results of thedifferential thermo-analysis (DTA), it is also seen that the losses inweight near 400° C. and more than 700° C. are each due to emission ofoxygen and Tl.

FIG. 5 is a diagram showing that the hole density changes with thetemperature in the first form of embodiment of the invention.

As shown in FIG. 5, the carriers for Cu found from measurement of Hallcoefficient has a density of 0.5 at the temperature of 300 K for aspecimen as it is formed by high pressure synthesis, which leaves thespecimen over-doped. However, annealing changes the carrier density.Thus, while annealing at 400° C. reduces the carrier density to 0.12 andbrings the specimen into an under-doped state, annealing at 540° C.gives rise to a carrier density of 0.2 and brings the specimen almostinto an optimum-doped state. FIG. 6 is a diagram showing relationshipsbetween Tc of a specimen in the first form of embodiment of theinvention annealed, its normally conducting electrical resistivity,carrier density and weight's rate of change and the annealingtemperature.

Referring to FIG. 6, annealing a specimen in an over-doped state causesoxygen to come out of it, resulting in a decreases in its carrierconcentration and hence a rise in Tc. At the annealing temperature of400° C., oxygen coming off radically brings the specimen into anunder-doped state while maintaining Tc high.

A rise further in the annealing temperature further decreases the oxygenconcentration, but is followed by a change in electronic state whichincreases the carrier concentration so it nears its optimum dopingamount. And at the annealing temperature of 540° C., Tc becomes itsmaximum. And ye, at any temperature of 700° C. or more, oxygen furthercoming off causes the specimen to deteriorate.

The phenomenon that a change in electronic state increases the carrierconcentration has been mentioned before in connection with FIGS. 7 and8, and can be explained as follows: To wit, Tl ions present in chargesupply layers are trivalent (+3) and Tl6 s level lies above the Fermilevel (Es) if the oxygen concentration is high. As the oxygenconcentration lowers, Tl ions are reduced to become monovalent (+1) andthe Tl6 s level becomes lower than the Fermi level. This causes Tl ionsto pull electrons out of the 5-coordination CuO₂ surface that is asuperconducting layer and conversely to supply the superconducting,5-coordination CuO₂ surface with holes.

In this manner, selective reduction of Tl ions can supply holes, therebyincreasing the carrier concentration.

It should be noted at this point that from measurement of changes in theupper critical magnetic field, a selective reduction type hightemperature superconductor is found to have coherence length of 3 Å ormore. Also, from measurement of the ratio of the upper critical magneticfield in the c-axis to those in the a- and b-axes, its superconductinganisotropy is found to be 10 or less.

Mention is next made of a second, preferred form of embodiment of theinvention.

This second form of embodiment is a thin film of a selective reductiontype high temperature superconductor having a composition:(Cu_(1−x)Tl_(x))(Ba, Sr)₂Ca₂Cu₃O_(y) with the structure, like that ofthe afore-mentioned first form, as shown FIG. 2A.

Continued, an explanation is given in respect of a method of making forthe second form of embodiment.

First, a precursor component Cu—Ba—Ca—O has Tl₂O₃ uniformly mixedtherewith in an amount of 0.25 to 0.5 mol to prepare:

Cu_(1−x)Tl_(x)Ba₂Ca₃Cu₄O_(y) where x=0.25 to 0.5, and by pressing toform thallium mixed pellets each of a diameter of 10 mm and a weight ofabout 450 mg.

Next, such a thallium mixed pellets is pre-heated for 1 hour to preparea pellet for thallium adjustment.

Next, a SrTiO₃ substrate has an amorphous film of (Cu_(1−x)Tl_(x))(Ba,Sr)₂Ca₂Cu₃O_(y) built up thereon by RF magnetron spattering using, forexample, a sintered TlBaSrCa₂Cu₃O_(y) body as a target.

Subsequently, the SrTiO₃ substrate having the amorphous film built upthereon, the thallium mixed pellet and the pellet for thalliumadjustment are encapsulated in a capsule made of Au, Ag or Pt and thenare heat-treated at a temperature of 860° C. to 890° C. for a period of30 to 90 minutes to cause an epitaxy film of (Cu_(1−x)Tl_(x))(Ba,Sr)₂Ca₂Cu₃O_(y) to epitaxially grow from the amorphous film. Thisprocess will be referred to below as “amorphous phase epitaxy (APE)process”.

The superconductor film of (Cu_(1−x)Tl_(x))(Ba, Sr)₂Ca₂Cu₃O_(y) obtainedby the APE process is annealed in a low oxygen gaseous atmosphere of 1atm or less at a temperature of 500° C. for a period of 30 minutes toprepare a selective reduction type, high temperature superconductor ofthe composition with x=0.4 to 0.8 as the second form of embodiment ofthe invention.

It should be noted here that the method of making described above forthe second form of embodiment is applicable to a (Cu, M) family, hightemperature superconductor as well with the composition formula (c)mentioned in connection with the first form of embodiment of theinvention. Here again as there, selective reduction can yield a positivehole dopable, high temperature superconductor.

The second form of embodiment of the invention is advantageous in thatit gives rise to Jc that is so high as Jc=1×10⁶ to 2×10⁷ A/cm² (77K,OT).

FIG. 9 is a diagram showing an X-ray analysis pattern of a specimen inthe second form of the invention.

As shown in FIG. 9, a strong (001) peak is found, indicating that ac-axis orientation is the case. The c-axis here has a lattice constantof 15.89 Å that lies between 14.79 Å of a Cu-oxide high temperaturesuperconductor and 15.93 Å of Tl-oxide high temperature superconductor.

Also, from observation of X-ray culminating (peak, extreme) points ithas been confirmed that an in-plane orientation is the case (Δφ=0.5 to1.5 degree).

It has further been shown that the composition (Cu_(1−x)Tl_(x))(Ba,Sr)₂Ca₂Cu₃O_(y) y if annealed at a temperature of 870 to 900° C. for aperiod of 30 to 90 minutes has Tc=96 to 115 K and Jc=1×10⁶ to 2×10⁷A/cm² (77K, OT).

Mention is next made of a third, preferred form of the presentinvention. The selective reduction type high temperature superconductorin the third form of embodiment is a superconductor film of n=4, thecomposition Cu_(1−x)Tl_(x)Ba₂Ca₃Cu₄O_(y) having a structure as shown inFIG. 2B. This structure as indicated in the Figure is referred to hereinas Cu-1234.

An explanation is given in respect of a method of making asuperconductor in the third form of embodiment of the invention.

A SrTiO₃ substrate has an amorphous film of(Cu_(1−x)Tl_(x))Ba₂Ca₃Cu₄O_(y) built up thereon by RF magnetronspattering using a sintered body composed ofCu_(1−x)Tl_(x)Ba₂Ca₃Cu₄O_(y) as a target.

The amorphous film, together with pellets as mentioned in connectionwith the second form of embodiment, in a capsule made of Au, Ag or Ptand then is heat-treated at a temperature of 880° C. to 920° C. for aperiod of 1 hour. Further, the heat-treated amorphous film after havingan electrode film of Au deposited thereon is annealed in a low oxygengaseous atmosphere of 1 atm or less at a temperature of 450 to 500° C.for a period of 30 minutes to prepare a selective reduction type hightemperature superconductor as the third form of embodiment of theinvention.

The preceding method used to make a superconductor in the third form ofembodiment is applicable to making a selective reduction type hightemperature superconductor that can be indicated by composition formula(d):

Cu_(1−x)Tl_(x)(Ba_(1−y)Sr_(y))₂(Ca_(1−z)L_(z))₃Cu₄O_(12−w)

where L represents one or more elements selected from the class whichconsists of Mg and alkaline metallic elements; 0≦x≦1.0; 0≦y≦1; 0≦z≦1;and 0≦w≦4.

An explanation is next given in respect of properties of a selectivereduction type high temperature superconductor according to the thirdform of embodiment of the present invention.

X-ray analysis of the thin film shows that it has a lattice constant of18.9 to 18.5 Å that lies between 17.99 Å of Cu-1234 and 19.11 Å ofTl-1234.

The X-ray peak pattern has a half-width Δ=0.5 to 1.5, indicating a goodorientation in the a-b plane.

Further, from composition analysis by an energy distribution typecomposition analyzer (EDX), it has been found that x=0.4 to 0.8 and frommeasurement of electrical resistivity Tc has been found to be 100 to 115K. Jc has been found to lie between 1 and 2×10⁶ A/cm². Improving thepreparation process may further rise both Tc and Jc.

While a method of making a selective reduction type, high temperaturesuperconductor according to the present invention permits changing n byits preparation composition or the preparation composition of the targetmaterial, it should be noted that the n can be changed by changing thereaction temperature and the treatment time period as well. A selectivereduction type high temperature superconductor of optimum properties hascurrently been found to be obtainable with n of 4 to 6 and a thicknessof unit lattice (CaCuO₂)_(n) of 10 to 16 Å.

Although the present invention has hereinbefore been set forth withrespect to certain illustrative forms of embodiments thereof, it willreadily be appreciated to be obvious to a person skilled in the art thatmany alternations thereof, omissions therefrom and additions thereto canbe made without departing from the essences of scope of the presentinvention. Accordingly, it should be understood that the invention isnot intended to be limited to the specific forms of embodiment thereofset forth below, but to include all possible forms of embodiment thereofthat can be made within the scope with respect to the featuresspecifically set forth in the appended claims and encompasses all theequivalents thereof.

Industrial Applicability

As has been set forth in the foregoing description, a selectivereduction type high temperature superconductor and a method of makingthe same according to the present invention are extremely useful in thesuperconducting electronics industry that involves large scalesuperconducting power transmission, superconducting power storage orreserve, superconducting electronic components such as a highperformance Josephson device, a high frequency device or the like.

What is claimed is:
 1. A selective reduction type high temperaturesuperconductor, characterized in that the high temperaturesuperconductor has a unit cell that comprises a pair of charge supplylayers formed by an upper and a lower surface thereof having each of aportion of Cu atoms substituted with a selectively reducible atom, andsuperconducting layers as layers other than said charge supply layers,wherein said charge supply layers have said selectively reduced atomsselectively reduced, characterized in that the superconductor is made ofa (Cu, M) family high temperature superconducting material that can bedescribed by composition formula:Cu_(1−x)M_(x)(Ba_(1−y),Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w)where M represents ions of one or more polyvalent metallic elementsselected from the class which consists of Tl, Bi, Pb, In, Ga, Sn, Ti, V,Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, W, Re and Os; L represents one or moreelements selected from the class which consists of Mg and alkalinemetallic elements; 0≦x≦1.0; 0≦y≦1; 0≦z≦1; 0≦w≦4; and 1≦n≦16.
 2. Aselective reduction type high temperature superconductor as set forth inclaim 1, characterized in that selective reduction as aforesaid of saidhigh temperature superconductor forms in said superconducting layers ofthe high temperature superconductor a first and a second region whichare doped overly and doped optimally, respectively, with superconductingcarriers.
 3. A selective reduction type high temperature superconductoras set forth in claim 1 or claim 2, characterized in that selectivereduction as aforesaid of said high temperature superconductor maintainsa superconducting carrier concentration in said superconducting layersinto as doped overly or as doped optimally with the superconductingcarriers.
 4. A selective reduction type high temperature superconductoras set forth in claim 1 or 2, characterized in that said superconductinglayers of said high temperature superconductor have an upper and a lowersurface constituted by a CuO₂ surface of a 5-coordination and a surfaceother than the upper and lower constituted by a CuO2 surface of a4-coordination.
 5. A selective reduction type high temperaturesuperconductor as set forth in claim 1 or 2, characterized in that it ismade of a (Cu, Tl) family high temperature superconducting material thatcan be described by composition formula:Cu_(1−x)Tl_(x)(Ba_(1−y),Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w)where L represents one or more elements selected from the claims whichconsists of Mg and alkaline metallic elements; 0≦x≦1.0; 0≦y≦1; 0≦z≦1;0≦w≦4; and 1≦n≦16.
 6. A selective reduction type high temperaturesuperconductor as set forth in claim 1 or claim 2, characterized in thatit is made of a (Cu, Tl) family high temperature superconductingmaterial that can be described by composition formula:Cu_(1−x)Tl_(x)(Ba_(1−y),Sr_(y))₂(Ca_(1−z)L_(z))₂Cu₃O_(10−w) where Lrepresents one or more elements selected from the class which consistsof Mg and alkaline metallic elements; 0≦x≦1.0; 0≦y≦1; 0≦z≦1; and 0≦w≦4.7. A selective reduction type high temperature superconductor as setforth in claim 1 or claim 2, characterized in that it is made of a hightemperature superconducting material that can be described bycomposition formula:Cu_(1−x)Tl_(x)(Ba_(1−y),Sr_(y))₂(Ca_(1−z)L_(z))₃Cu₄O_(12−w) where Lrepresents one or more elements selected from the class which consistsof Mg and alkaline metallic elements; 0≦x≦1.0; 0≦y≦1; 0≦z≦1; and 0≦w≦4.8. A selective reduction type high temperature superconductor as setforth in claim 1 or claim 2, characterized in that the concentration ofsuperconducting carriers is adjusted by selective reduction or byvarying (increasing or decreasing) oxygen concentration.
 9. A selectivereduction type high temperature superconductor as set forth in claim 1,characterized in that it is a selectively over-doped type or aselectively optimum-doped type, high temperature superconductor in whichn is any one of 3, 4, 5, 6, and
 7. 10. A selective reduction type hightemperature superconductor as set forth in claim 1 or claim 2,characterized in that selective reduction causes said substitutionalatoms in a said charge supply layer to receive electrons in their outershell orbits, thereby providing holes in the CuO₂ surface of5-coordination of said superconducting layer.
 11. A selective reductiontype high temperature superconductor as set forth in claim 1 or claim 2,characterized in that it has a superconducting anisotropy of not greaterthan 10, and a coherence distance of not less than 3 angstroms.
 12. Aselective reduction type high temperature superconductor as set forth inclaim 1 or claim 2, characterized in that said selective reductiontransforms its natural superconducting wave function that is of a d-waveto a wave function of a (d+is) wave that has also a property of ans-wave.
 13. A method of making a selective reduction type hightemperature superconductor, characterized in that it comprises the stepsof: adding an element exhibiting a self-assembling effect and selectivereducibility to a raw material of a high temperature superconductor;using the self-assembling effect of said element to cause a crystal ofhigh temperature superconductor to grow with a structure in which saidelement is substituted for a portion of Cu atoms in a charge supplylayer of a basic cell of the high temperature superconductor; and usingthe selective reducibility of said element to selectively reduce saidelement in the charge supply layer of the basic cell of said hightemperature superconductor crystal, characterized in that thesuperconductor is made of a (Cu, M) family high temperaturesuperconducting material that can be described by composition formula:Cu_(1−x)M_(x)(Ba_(1−y),Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w)where M represents ions of one or more polyvalent metallic elementsselected from the class which consists of Tl, Bi, Pb, In, Ga, Sn, Ti, V,Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, W, Re and Os; L represents one or moreelements selected from the class which consists of Mg and alkalinemetallic elements: 0≦x≦1.0; 0≦y≦1; 0≦z≦1; 0≦w≦4; and 1≦n≦16.
 14. Amethod of making a selective reduction type high temperaturesuperconductor as set forth in claim 13, characterized in that: the stepof causing the high temperature superconductor crystal to grow includesthe step of admixing together a precursor of the high temperaturesuperconductor, a chemical compound of said element and a oxidizing anda reducing agent to form a mixture thereof, and heat treating saidmixture in a high pressure condition; and the step of selectivereduction comprises heat treating said high temperature superconductorcrystal in a reducing atmosphere.
 15. A method of making a selectivereduction type high temperature superconductor as set forth in claim 14,characterized in that: said mixture comprises a mixture formed byadmixing said precursor represented by composition formula: Ba₂Ca₂Cu₃O₇,said element chemical composition constituted by Tl₂O₃, said oxidizingagent constituted by AgO or CaO₂ and said reducing agent constituted byCu₂O with a prepared composition: Cu_(0.5)Tl_(0.5)Ba₂Ca₂Cu₃O_(y); thestep of causing high temperature superconductor to crystallographicallygrow includes a heat treatment under a high pressure of 5 Gpa at atemperature of 850° C. for a period of 2 hours; and the step ofselective reduction includes a heat treatment at a temperature of 400 to700° C., preferably at 540° C., for a period of 12 hours in a reducingatmosphere in N₂; thereby forming a selective reduction type hightemperature superconductor having a Cu-1223 structure and represented bycomposition formula: (Cu_(1−x)Tl_(x))Ba₂Ca₂Cu₃O_(y) where 0≦x≦1.0 and0≦y≦1.
 16. A method of making a selective reduction type hightemperature superconductor as set forth in claim 14, characterized inthat: the precursor of said high temperature superconductor is aprecursor represented by composition formula:Cu(Ba_(1−y)Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w) where Lrepresents one or more elements selected from the class which consistsof Mg and alkaline metallic elements; 0≦x≦1.0; 0≦y≦1; 0≦z≦1; 0≦w≦4; and1≦n≦16; and the chemical compound of said element exhibiting saidself-assembling effect and said selective reducibility is a compoundcontaining one or more polyvalent metallic elements selected from theclass which consists of Tl, Bi, Pb, In, Ga, Sn, Ti, V, Cr, Mn, Fe, Co,Ni, Zr, Nb, Mo, W, Re and Os; thereby forming a selective reduction typehigh temperature superconductor having a Cu-1223 structure andrepresented by composition formula:Cu_(1−x)M_(x)(Ba_(1−y)Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w.) 17.A method of making a selective reduction type high temperaturesuperconductor, characterized in that it comprises the steps of: heattreating in an atmosphere of an element exhibiting a self-assemblingeffect and a selective reducibility an amorphous film of a hightemperature superconductor composition containing said element depositedon a single crystalline substrate; using the self-assembling effect ofsaid element and an epitaxy effect of said single crystalline substrateto cause a high temperature superconductor to crystallographically growwith a structure having said element substituted for a portion of Cuatoms in a charge supply layer of a basic cell of the high temperaturesuperconductor; and using the selective reducibility of said element toselectively reduce said element in the charge supply layer of the basiccell of said high temperature superconductor, characterized in that thesuperconductor is made of a (Cu, M) family high temperaturesuperconducting material that can be described by composition formula:Cu_(1−x)M_(x)(Ba_(1−y),Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w)where M represents ions of one or more polyvalent metallic elementsselected from the class which consists of Tl, Bi, Pb, In, Ga, Sn, Ti, V,Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, W, Re and Os; L represents one or moreelements selected from the class which consists of Mg and alkalinemetallic elements: 0≦x≦1.0; 0≦y≦1; 0≦z≦1; 0≦w≦4; and 1≦n≦16.
 18. Amethod of making a selective reduction type high temperaturesuperconductor as set forth in claim 17, characterized in that: the stepof causing said high temperature superconductor to crystallographicallygrow includes the steps of preparing a mixture pellet containing saidelement and a pellet for adjusting the concentration of said element,depositing said amorphous film on said single crystalline substrate byspattering a target of a high temperature superconductor compositioncontaining said element, and heat treating said mixture pellet, saidconcentration adjustment pellet and said amorphous film commonly in aclosed container; and the step of selective reduction includes heattreating said high temperature superconductor crystal in a reducingatmosphere.
 19. A method of making a selective reduction type hightemperature superconductor as set forth in claim 18, characterized inthat: said mixture pellet is a mixture of a high temperaturesuperconductor precursor whose constituent elements are Cu, Ba, Ca and Owith Tl₂O₃ as a chemical compound of said self-assembling effect andselective reducibility exhibiting element in a composition rangeexpressed by composition formula: Cu_(1−x)Tl_(x)Ba₂Ca₃Cu₄O_(y) wherex=0.25 to 0.5 and formed by pressing; said concentration adjustmentpellet is a thallium concentration adjustment pellet formed by heattreating a said mixture pellet for a period of 1 hour; said amorphousfilm is obtained by spattering a sintered target of a compositionexpressed by composition formula: TlBaSrCa₂Cu₃O_(y) to deposit thecomposition on a SrTiO₃ substrate; the heat treatment in said closedcontainer is performed at a temperature of 860 to 900 for a period of 30to 90 minutes; the step of selective reduction include a heat treatmenteffected at a temperature of 500° C. for a period of 30 minutes in areducing atmosphere of a low pressure oxygen gas at a pressure not inexcess of 1 atm; and thereby forming a selective reduction type hightemperature superconductor having a Cu-1223 structure and expressed bycomposition formula: (Cu_(1−x)Tl_(x))(BaSr)₂Ca₂Cu₃O_(y) where x=0.4 to0.8.
 20. A method of making a selective reduction type high temperaturesuperconductor as set forth in claim 18, characterized in that: saidmixture pellet is a mixture of a high temperature superconductorprecursor whose constituent elements are Cu, Ba, Ca and O with achemical compound containing one or more of self-assembling effect andselective reducibility exhibiting elements as aforesaid M selected fromthe class which consists of Tl, Bi, Pb, In, Ga, Sn, Ti, V, Cr, Mn, Fe,Co, Ni, Zr, Nb, Mo, W, Re and Os in a composition range expressed bycomposition formula: Cu_(1−x)M_(x)Ba₂Ca₃Cu₄O_(y) where x=0.25 to 0.5 andformed by pressing; said concentration adjustment pellet comprises an Mconcentration adjustment pellet formed by heat treating a said mixturepellet for a period of 1 hour; said target is a sintered target of acomposition expressed by composition formula: TlBaSrCa₂Cu₃Oy; andthereby forming a (Cu, M) family, selective reduction type hightemperature superconductor having a Cu-1223 structure and expressed bycomposition formula:Cu_(1−x)M_(x)(Ba_(1−y)Sr_(y))₂(Ca_(1−z)L_(z))_(n−1)Cu_(n)O_(2n+4−w.) 21.A method of making a selective reduction type high temperaturesuperconductor as set forth in claim 18, characterized in that: saidmixture pellet is a mixture of a high temperature superconductorprecursor whose constituent elements are Cu, Ba, Ca and O with Tl203 asa chemical compound of said self-assembling effect and selectivereducibility exhibiting element in a composition range expressed bycomposition formula: Cu_(1−x)Tl_(x)Ba₂Ca₃Cu₄O_(y) where x=0.25 to 0.5and formed by pressing; said concentration adjustment pellet is athallium concentration pellet formed by heat treating a said mixturepellet for a period of 1 hour; said amorphous film is obtained byspattering a sintered target of a composition expressed by compositionformula: Cu_(1−x)Tl_(x)Ba₂Ca₃Cu₄O_(y) to deposit the composition on aSrTiO₃ substrate; the heat treatment in said closed container isperformed at a temperature of 880 to 920° C. for a period of 60 minutes;the step of selective reduction include a heat treatment effect at atemperature of 450 to 500° C. for a period of 30 minutes in a reducingatmosphere of low pressure oxygen gas at a pressure not in excess of 1atm; and thereby forming a selective reduction type high temperaturesuperconductor having a Cu-1234 structure and expressed by compositionformula: Cu_(1−x)Tl_(x)Ba₂Ca₃Cu₄O_(y).
 22. A method of making aselective reduction type high temperature superconductor as set forth inclaim 18, characterized in that: said mixture pellet is a mixture of ahigh temperature superconductor precursor whose constituent elements areCu, Ba, Ca and O with Tl203 as a chemical compound of saidself-assembling effect and selective reducibility exhibiting element ina composition range expressed by composition formula:Cu_(1−x)Tl_(x)Ba₂Ca₃Cu₄O_(y) where x=0.25 to 0.5 and formed by pressing;said concentration adjustment pellet is a thallium concentrationadjustment pellet formed by heat treating a said mixture pellet for aperiod of 1 hour; said amorphous film is obtained by spattering asintered target of a composition expressed by composition formula:Cu_(1−x)Tl_(x)(Ba_(1−y)Sr_(y))₂(Ca_(1−z)L_(z))₃Cu₄O_(12−w) to depositthe composition a SrTiO3 substrate; and thereby forming a selectivereduction type high temperature superconductor having a Cu-1234structure and expressed by composition formula:Cu_(1−x)Tl_(x)(Ba_(1−y)Sr_(y))₂Ca₃Cu₄O_(y) where 0≦x≦1.0 0≦y≦1; 0≦z≦1;and 0≦w≦4.